Radio communication system



Feb. 18, 1941. A. ALFORD 2,232,043

RADIO COMMUNICATION SYSTEM Filed 001;. 11, 1939 FIGJ.

INVENTOR A/Vfl/QEW AL FORD ATTOR N EY Patented Feb. 18, 1941 UNITED STATES PATENT OFFICE RADIO COIVHVIUNICATION SYSTEM Application October 11, 1939, Serial No. 298,905

8 Claims.

This invention relates to radio communication systems and more specific-ally to a system for varying the modulation effect on aircraft radio receivers or transmitter, produced by the propellers of said aircraft.

An object of the invention is to detune the aircraft propeller and thereby vary the distortion of the field pattern in the vicinity of said propeller.

It is well known in the art that antennas and/ or conductors cause a distortion in a radiant action pattern in their immediate vicinity, the amount of distortion depending on the tuning of the conductor with respect to the frequency of the radiation as well as on the orientation of the conductor with respect to the radiation. This effect is especially noticeable and undesirable in the operation of antennas on aircraft provided with metal propellers. The rotating propeller changes the radiation field pattern surrounding it at a regular rate, said change modulating the signal represented by said radiation.

In aircraft communication systems at high frequencies the propeller may be of such a length to vicinity of said propeller so that any change in the tuning of the electrical means also changes the effect of the propeller upon the radiant action pattern.

In order to illustrate the :above features reference may be made to the attached drawing wherein:

Fig. 1 illustrates in side elevation a propeller detuning means according to the invention;

Fig. 2 illustrates in side elevation an electromagnetic detuning means according to the invention;

Fig. 3 illustrates in side elevation an electrostatic detuning means according to the invention.

Fig. 1 illustrates a propeller l which interferes with the field pattern of antenna system 2 of airplane 6 when it is substantially parallel to the direction of effective polarization of said antenna. A tunable dipole antenna means 3 is located parallel to such direction of effective polarization of antenna system 2 and in the vicinity of propeller l and is used to change the effective tuning of said propeller so that the effect of said propeller upon the field pattern is varied.

Fig. 2 similarly illustrates propeller l, antenna system 2, and a tunable electrical means 5 electromagnetically coupled to said propeller.

Fig. 3 similarly illustrates propeller I, antenna system 2, and a tunable electrical means 5 electrostatioally coupled to said propeller.

It is evident that when signals are polarized in the. plane of antenna system 2, the said propeller will cause greatest interference when in a common plane with said antenna. In the case where the antenna system is of a complex nature or the antenna system is not polarized it may be desirable to locate the detuning apparatus so that the effect of said propeller will be reduced when the propeller is parallel to the direction of polarization of the signal.

It will also be understood that several tunable electrical means may be used to provide for changing the effect of the propeller as the propeller assumes Various positions about its axis, or a single means may be provided that may be rotated about an axis.

While I have described particular embodiments of my invention for purposes of illustration, it will be understood that various modifications and adaptations thereof may be made Within the spirit of .the invention as set forth in the appended claims.

What is claimed is:

1. A radio communication system comprising an aircraft having a rotatable metal propeller of such a length as to substantially resonate at the communication frequency, an antenna mounted on said aircraft and positioned with respect to said propeller so that a distorting effect is produced on the radiant action pattern of said antenna in certain positions of said propeller, and electrical means mounted on said aircraft for detuning said propeller to modify said distorting effect in at least one of said certain positions.

2'. A radio communication system comprising an aircraft having a rotatable met-a1 propeller substantially resonant at the communication frequency, an antenna mounted on said aircraft and positioned with respect to said propeller so that a distorting effect is produced on the radiant action pattern of said antenna in certain positions of said propeller, andelectrical means rotatably adjustable about an axis mounted on said aircraft for detuning said propeller to modify said distorting effect in any of said certain positions.

3. A radio communication system comprising an aircraft having a rotatable metal propeller substantially resonant at the communication frequency, an antenna mounted on said aircraft and positioned with respect to said propeller so that a distorting effect is produced on the radiant action pattern of said antenna in certain positions of said propeller, and tunable electrical means for detuning said propeller mounted on said aircraft for modifying said distorting effect in at least one of said certain positions.

4. A radio communication system comprising an aircraft having a rotatable metal propeller substantially resonant at the communication frequency, an antenna mounted on said aircraft and positioned with respect to said propeller so that a distorting effect is produced on the radiant action pattern of said antenna in certain positions of said propeller, and electrical means electrostatically coupled to said propeller and mounted on said aircraft for modifying said distorting effect in at least one of said certain positions.

5. A radio communication system comprising an aircraft having a rotatable metal propeller substantially resonant at the communication frequency, an antenna mounted on said aircraft mounted on said aircraft for modifying said distorting effect in at least one of said certain positions.

6. A radio communication system comprising 35: an aircraft having a rotatable metal propeller substantially resonant at the communication frequency, an antenna mounted on said aircraft and positioned with respect to said propeller so that a distorting effect is produced on the radiant action pattern of said antenna in certain positions of said propeller, and electrical means substantially parallel to the direction of polarization of said radiant action for detuning said propeller mounted on said aircraft for modifying said distorting effect.

'7. A radio communication system comprising an aircraft having a rotatable metal propeller substantially resonant at the communication frequency, an antenna mounted on said aircraft and positioned with respect to said propeller so that a distorting effect is produced on the radiant action pattern of said antenna in certain positions of said propeller, and dipole antenna means substantially parallel to the direction of polarization of said radiant action mounted on said aircraft for modifying said distorting effect.

8. A radio communication system comprising an aircraft having a rotatable metal propeller substantially resonant at the communication frequency, an antenna mounted on said aircraft and positioned with respect to said propeller so that a distorting effect is produced on the radiant action p-attem of said antenna in certain positions of said propeller, and tunable dipole antenna means substantially parallel to the direction of polarization of said radiant action mounted on said aircraft for modifying said distorting effect. v

ANDREW ALFORD. 

